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is the title of an excellent book by Jerry Weinberg. As usual I'm going to quote from a few pages:

Software development is not primarily a manufacturing operation for we (ideally) never develop the same software twice. This uniqueness of product means that Deming's "statistical signal" - though necessary - is not sufficient for feedback control, because there often isn't enough repetition - enough stability - to generate meaningful statistics.

In software we are attempting to obtain value by achieving higher precision than human beings have ever attempted before.

The switch from cost observation to value observation is the strongest indication that an organization has made the transition from Pattern 2 (Routine) to Pattern 3 (Steering).